One example of a corrugated fin is depicted in FIG. 15. Note that the corrugated fin depicted in the drawing is an example of a plate fin where ribs are erected perpendicular to a plate-like body. The corrugated fin 10 has a plurality of consecutive ribs 12 formed in a metal plate-like body 9 made of aluminum or the like, and is mainly used in a heat exchanger in a vehicle radiator, an air conditioner, an EGR, or the like.
The construction disclosed in Patent Document 1 can be given as one example of a manufacturing apparatus for manufacturing the corrugated fin 10. This manufacturing apparatus is capable of molding the ribs one at a time in a single pressing where a punch and a die are closed by a single press operation of a press apparatus.
When manufacturing the corrugated fin 10, the plate-like body used as a material is drawn in between the punch and die, and if a plurality of punches and dies are used to simultaneously mold a plurality of ribs, the plate-like body will become pulled at both ends between the adjacent punches and dies, resulting in the risk of thinning and snapping of the ribs. For this reason, it has been difficult to simultaneously operate a plurality of punches and dies to simultaneously mold a plurality of ribs.
On the other hand, Patent Document 2 discloses a construction where the die is divided in the horizontal direction and is provided so as to be movable. With this construction, since the die that moves in the horizontal direction holds the side surfaces of the ribs, thinning and snapping of the ribs due to the plate-like body being pulled at both ends between the punches and dies are prevented.
FIG. 16 depicts a conventional corrugated fin manufacturing apparatus for forming one rib by a single mold closing operation.
On the downstream side in the conveying direction of the plate-like body 9, a pilot punch 13a is disposed on the upper mold so as to be energized downward by an energizing means such as a spring. When a mold closing operation begins, the pilot punch 13a is lowered before the other punch and, in combination with the die of the lower mold, enters a rib that has already been formed by the previous mold closing operation to position the plate-like body 9.
A machining punch 13b is disposed upstream of the pilot punch 13a so as to be energized downward by an energizing means such as a spring. When a mold closing operation begins, the machining punch 13b is lowered following the pilot punch 13a to press the plate-like body 9 that has been positioned by the pilot punch 13a onto the die 16 of the lower mold and thereby form a rib. A pressing portion 15 for applying pressure from above onto a part of the plate-like body 9 that has not been machined into ribs is formed on the upstream-side surface of the machining punch 13b. 
A plurality of concaves are formed in the die 16 of the lower mold. A concave that is downstream in the conveying direction of the plate-like body 9 is a pilot concave 16a into which the pilot punch 13a enters. A machining concave 16b into which the machining punch 13b enters to machine a rib is formed on the upstream side of the pilot concave 16a. A mounting portion 17 with a flat upper surface onto which a lower surface of the unmachined part of the plate-like body 9 that is pressed by the pressing portion 15 of the machining punch 13b is mounted is formed on the upstream side of the machining concave 16b. 
Since the plate-like body 9 is pulled between the machining punch 13b and the machining concave 16b of the die while the machining punch 13b and the machining concave 16b are forming a rib 12, the part that has not been machined into ribs bends upward. From the formation of a rib 12 onwards, the pressing portion 15 of the machining punch 13b gradually presses the upwardly bent unmachined part downward toward the die so that at a bottom dead center, the unmachined part is pressed between the pressing portion 15 of the machining punch 13b and the mounting portion 17 of the die 16, resulting in the unmachined part becoming flat.